The invention relates to a radiation chopper having a chopper disk disposed in a chopper chamber between a first housing part and a second housing part. The front part has a support for a cell containing the substance to be analyzed, and the rear part has a mount for a radiation source directed toward the cell.
Optical chopper disks are preferably used in analytical devices for determining the absorption capacity of a solid, liquid or gaseous substance.
The purpose of such disks is to shortly interrupt one or several light beams that directly or indirectly impinge on a light-sensitive sensor. This interruption and the subsequent release of the light beam is also referred to as light modulation.
In many cases this light modulation serves to separate the actual measuring signal from interfering signals. In multi-channel analytical devices a chopper disk can be used to interrupt or release the light in a first channel at a first time and the light in a second channel at a second time.
Choppers are already known for devices for measuring the optical absorption capacity which includes a Ferraris-motor comprising one chopper disk and two electromagnetic systems (German OS 26 08 669, to which U.S. Pat. No. 4,155,010 corresponds). When choppers of this kind are realized, it turned out that the chopper disk easily becomes skewed and is subject to a temperature drift.
Further, a chopper of the kind in question (German OS 37 23 177) is known where the chopper disk is disposed between two housing parts that are on top of each other. The one part has a bearing whereas the other part has an recess in which the bearing can be introduced. An additional recess is disposed on the side of the one part of the housing which faces the other part. The depth of this recess essentially corresponds to the thickness of the chopper disk. This part is provided with a bearing for the one end of a shaft supporting the chopper disk.